Sarah Reichelt (@troz@mastodon.social) published a short guide on how app permissions on macOS Sequoia work with unsigned apps, and how you can run them anyway.

The context menu trick doesn’t seem to work anymore, and you need to go to System Settings, it seems. (I’m not yet on Sequioa.)

TL;DR: You can still run unsigned apps, but it’s a bit more difficult. After trying once, you have to go to System Settings → Privacy & Security, scroll to the end and click Open Anyway for that app.